The present invention concerns a force compensation device for a cable control of a gearshift for a cycle.
There currently exist speed change units of the type including:
a control device, such as an operating handle, lever or even a rotating handle secured to the frame immediately close to the handlebar and able to be maneuvered by the user,
a control cable, and
a gearshift composed of a plate secured to the frame, a mobile parallelogram type element for guiding the chain able to be moved laterally, and a spring for bringing this mobile guiding element into one of the extreme positions.
In the case of a rear gearshift ensuring the change of gears, the mobile element is a deformable parallelogram which deviates from the hub bearing the gears under the recall effect of the spring and which moves closer to it under the traction action of the cable when the user exerts pressure on the control device.
In the case of gears, the jump from one gear to the other for changing up the smallest to the largest remains with a relatively slight amplitude as the gears are fully stepped, with the result that, although difficult, the force still remains reasonable, but it is necessary to stretch the recall spring so that on return it can free the stored energy.
In plates, the case is otherwise. The smallest plate is on the side of the frame, and the guiding element, also in the form of a deformable parallelogram, is brought back to the frame and the maneuver member is activated by the user so as to move from the smallest to the largest plate. The difference of diameter is here much larger and the force to be provided is much greater.
In addition, it is to be noted that when the user wants to move from the largest plate to the lower plate, it is firstly necessary to mount the chain beyond the diameter of the large plate in question at the top of the teeth and no longer at the throat bottom, which requires an additional force when one is clearly looking for a means to reduce the force to be provided. This means having to provide a high-capacity elastic spring so as to resolve the corresponding difficult point.
As regards lifting a lower plate towards a higher plate, the user is obliged to overcome this difficult point and secondly he needs to compress the spring which requires that strong forces be exerted on the operating handle, lever or rotating handle to the detriment of accuracy of movement, attention when riding or concentration during a competitive race. It has even been observed that this becomes prohibitive for children or certain persons possessing moderate physical strength. In all cases, it is certain that the user tends to add a movement of the body to compensate which more or less makes him lose his balance and when this maneuver of the gearshifts is effected dozens of times, indeed several hundreds of times when going for a trip, one can understand the advantage in being able to control the required maneuver force.
The aim of the invention is to offer a force compensation device for a cable control of a gearshift for a cycle which favours user actions by balancing the actions, both for the change of speeds up and down, which reduces costs, is adaptable to existing systems, has little effect on the weight, occupies a smaller amount of space and is fully able to be integrated, both from the ergonomic and aesthetic points of view.
To this effect, the force compensation device of the invention for a cable control of at least one chain gearshift secured to the frame of a cycle with several plates and/or gears, the cable including an extremity integral with the gearshift and an extremity integral with a control device with a lever, handle or rotating handle generating a translation movement, this cable sliding into a sheath in support on a stop, the gearshift being equipped with a recall spring in a compressed state when the chain is on the largest plate or gear, wherein it includes at least one elastic element with an antagonistic recall effect disposed between a fixed stop integral with the cycle and a fixed stop integral with the cable, the elastic recall element being in a slackened state when the recall spring of the gearshift is in the compressed state and the recall element being in the compressed state when the recall spring of the gearshift is the slackened state.
This device is characterised in that the elastic recall element is a compensation spring disposed coaxial to the cable and inserted between a fixed stop integral with the frame and the extremity of this cable.
According to another characteristic, the compensation spring is a spring with a small diameter and a large number of contiguous spires in a compressed state, the force to compress it or the force restored being approximately equal to the force to compress or the force restored by the recall spring of the gearshift.
In the case of a monocontrol, the device of the invention includes two independent springs, each acting on the corresponding cable so as to obtain a compensation of the forces in all circumstances.
According to a particular embodiment, the compensation spring is integrated in an extension of the control member.
More specifically, in the case of a control member with a rotating handle, the compensation spring is a housing produced with the fixed handle grip.